Balancing comfort in a two-story home

Posted on Oct 01 2015 in Energy

by James Dulley

Duct Booster Fan

This cutaway photo shows how a duct booster fan is installed. It requires only a small section of the duct to be removed for installation.

We have a new heat pump, but we have a problem keeping all of the rooms in our home comfortable. Someone is always too hot or too cool. What are some simple methods to even out the temperatures throughout the house?

The problem you are experiencing is common, particularly in a two-story home — even for the newest heat pump systems. Unless you install an expensive zone-control system with multiple thermostats, your heat pump can only respond to the temperature of the room where the wall thermostat is located.

Numerous factors determine how much heating or cooling is used, and therefore the temperature is affected. These factors can include the number and orientation of the windows, whether the room is located on the first or second floor, the activity level in the room and the length of the duct leading to it.

There also may be differences in the energy efficiency of various rooms, which cause the temperature difference. Leaky windows are a particular problem. When using an air-conditioning system, place an air deflector over the register to help distribute cool air throughout the room.

The standard builder-installed sheet metal ductwork often has many leaky spots, so some of the heated or cooled air leaving the heat pump never makes it to the rooms in your home. The joints between the duct segments are the most common areas that leak. Use a high-quality duct sealant to seal the joints. You may find this takes care of most of the problem.

Check the ducts near the heat pump. If you see short handles on each one, they are for control dampers inside the ducts. When the handle is parallel to the duct, the damper is fully open. Partially close the dampers in the duct leading to the rooms which are getting too much heating or cooling to force more to the problem rooms.

Don’t try closing the damper in the room’s floor or wall registers. First, they typically are leaky, so the air flow will not be reduced by much. Second, because the ducts inside the walls are probably leaky and you have no access to seal them, conditioned air is lost inside the exterior walls.

If these methods do not provide adequate temperature balancing, consider installing duct booster fans. These small fans mount in the ducts to the problem rooms and force more conditioned air to them.

These fans are sized to fit standard round and rectangular residential ducts and can be controlled in different ways. The simplest fans sense when the main blower turns on, and they automatically run at the same time. Others have built-in thermostats to determine when they run. It is best to hire an experienced contractor to handle the installation for you. The fan can be wired into your blower switch to turn on with the heat pump.

A simple do-it-yourself option is to install a register booster fan. This small rectangular fan mounts over the register cover in the room and is plugged into a standard electrical wall outlet. The small fan uses only about 30 watts of electricity, and some models are adjustable to turn on only when more cooling or heating is needed in that particular room.

Setting the thermostat to continuous fan may also help, but note, it will increase your electric bill. The fan setting is most helpful if your new heat pump has a variable-speed blower, which allows the blower to continuously run on a low speed. Variable-speed blower motors are also more efficient than a standard blower motor.

James Dulley is a nationally syndicated engineering consultant based in Cincinnati. If you have a question about energy use or energy-efficient products, send it to: James Dulley, Electric Consumer, 6906 Royalgreen Drive, Cincinnati, OH 45244; or visit